The invention relates to digital image processing, and more particularly to image resampling methods and circuitry.
Modern digital video systems typically require resolution conversion capability for applications such as displaying HDTV signals at standard TV resolution, zooming, decimating, and providing picture-in-picture display. Poly-phase filtering allows accurate constant resampling ratios and may use predefined state machines to control pixel input pipelining and filter coefficient addressing according to predefined phase sequences. However, such filters are not flexible enough because they require adaptation each time a new conversion ratio is needed by a new application. Also, new video environment applications require new process capabilities such as frame rate conversions and play speed control. Those applications involve spatial field or frame interpolation capabilities that are usually offered with only a fixed number of predefined ratios, and this hinders vertical filtering.
Adams et al, A Monolithic Asynchronous Sample-Rate Converter for Digital Audio, ISCAS '93, pp. 1963–1966 (1993), disclose an integrated circuit providing audio sampling rate conversion with feedback tracking of the timing of output sample requests. This also shows experimental results for an input sampling rate of 48 KHz converted to an output sampling rate of 44.1 KHz.